1. Field of the Invention
This invention relates to a light source, and more particularly to a backlight assembly driving apparatus for a liquid crystal display. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for normally operating light emitting diodes in a backlight although a malfunction has occurred in one of the light emitting diodes.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) controls light transmittance of liquid crystal cells in accordance with video signals, to thereby display a picture. An active matrix type of liquid crystal display device uses a switching device in each liquid crystal cell so that each liquid cell can be actively switched. Such active switching increases response speed so that moving pictures can be displayed on the liquid crystal display device. The switching device used for the active matrix liquid crystal display device is typically a thin film transistor (TFT).
FIG. 1 is an equivalent circuit diagram of a pixel provided at a liquid crystal display device. A gate electrode of the TFT is connected to the gate line GL while a source electrode thereof is connected to a data line DL. Further, a drain electrode of the TFT is connected to a pixel electrode of the liquid crystal cell Clc and to one electrode of a storage capacitor Cst. A common electrode of the liquid crystal cell Clc is supplied with a common voltage Vcom. The active matrix LCD converts a digital input data into an analog data voltage on the basis of a gamma reference voltage. When the analog data voltage is supplied to the data line DL while a scanning pulse is supplied to the gate line GL, a channel between the source electrode and the drain electrode thereof, thereby supplying a data voltage on the data line DL to the pixel electrode to thereby charge the liquid crystal cell Clc. Thus, the storage capacitor Cst receives the data voltage fed from the data line DL when the TFT is turned ON, and then maintains the data voltage in the liquid crystal cell when the TFT is turned OFF. In response to the data voltage on the pixel electrode, liquid crystal molecules of the liquid crystal cell are reoriented by an electric field between the pixel electrode and the common electrode, to thereby modulate light.
FIG. 2 is a block diagram of a related art liquid crystal display device. As shown in FIG. 2, a liquid crystal display device 100 includes a liquid crystal display panel 110 having thin film transistors (TFTs) for driving the liquid crystal cells Clc adjacent to where data lines DL1-DLm and gate lines GL1-GLn crossing each other, a data driver 120 for supplying data to the data lines DL1-DLm of the liquid crystal display panel 110, a gate driver 130 for supplying a scanning pulse to the gate lines GL1-GLn of the liquid crystal display panel 110, a gamma reference voltage generator 140 for providing a gamma reference voltage to the data driver 120, a backlight assembly 150 for irradiating light onto the liquid crystal display panel 110, an inverter 160 for applying AC voltage and current to the backlight assembly 160, a common voltage generator 170 for providing a common voltage Vcom to the common electrode of the liquid crystal cells Clc of the liquid crystal display panel 110, a gate driving voltage generator 180 for providing a gate high voltage VGH and a gate low voltage VGL to the gate driver 130, and a timing controller 190 for controlling the data driver 120 and the gate driver 130. The liquid crystal display panel 110 has a layer of liquid crystal positioned between two glass substrates. The data lines DL1-DLm and the gate lines GL1-GLn perpendicularly cross each other on the lower glass substrate of the liquid crystal display panel 110. Each crossing of the data lines DL1-DLm and the gate lines GL1-GLn is provided with a TFT.
The TFTs of the liquid crystal display panel 110 switches data on the data lines DL1-DLm to the liquid crystal cells Clc in response to scanning pulses on the gate lines GL1-GLn. The gate electrode of a TFT is connected to gate lines while the source electrode thereof is connected to a data line. Further, the drain electrode of the TFT is connected to the pixel electrode of the liquid crystal cell Clc and to the storage capacitor Cst.
The gamma reference voltage generator 140 receives the highest level of power voltage VCC of the power voltage supplied to the liquid crystal display panel 110 to generate positive and negative gamma reference voltages, which are supplied to the data driver 120. The data driver 120 supplies data to the data lines DL1-DLm in response to a data driving control signal DDC from the timing controller 190. Further, the data driver 120 samples and latches a digital video data RGB fed from the timing controller 190, and then converts digital video data RGB into analog data voltages based upon a gamma reference voltage from the gamma reference voltage generator 140. The analog data voltages, which are representative of gray scale levels in the liquid crystal cell Clc of the liquid crystal display panel 110, are then supplied to the data lines DL1-DLm.
The gate driver 130 sequentially generates a scanning pulse, such as a gate pulse, in response to a gate driving control signal GDC and a gate shift clock GSC from the timing controller 190. The gate driver 130 provides a high level voltage and a low level voltage of the scanning pulse in accordance with the gate high voltage VGH and the gate low voltage VGL from the gate driving voltage generator 180. The scanning pulse is supplied to the gate lines GL1-GLn.
The backlight assembly 150 is provided at the rear side of the liquid crystal display panel 110, and is powered by an alternating current (AC) voltage supplied to the inverter 160. The backlight assembly 150 irradiates light onto each pixel of the liquid crystal display panel 110. The inverter 160 converts a rectangular wave signal generated within the inverter 160 into a triangular wave signal and then compares the triangular wave signal with a direct current (DC) power voltage VCC, to thereby generate a burst dimming signal proportional to a result of the comparison. If the burst dimming signal determined in accordance with the rectangular wave signal within the inverter 160, then a driving integrated circuit (IC) (not shown) for controlling a generation of the AC voltage within the inverter 160 controls a generation of AC voltage supplied to the backlight assembly 150 in response to the burst dimming signal.
The common voltage generator 170 receives a low-level power voltage VDD to generate a common voltage Vcom, and supplies it to the common electrode of the liquid crystal cell Clc provided at each pixel of the liquid crystal display panel 110. The gate driving voltage generator 180 is also supplied with a low-level power voltage VDD to generate the gate high voltage VGH and the gate low voltage VGL, which are supplied to the data driver 130. More particularly, the gate driving voltage generator 180 provides a gate high voltage VGH that is more than a threshold voltage of the TFTs in each of the pixels of the liquid crystal display panel 110 and a gate low voltage VGL that is less then the threshold voltage of the TFTs. The gate high voltage VGH and the gate low voltage VGL are used for determining a high level voltage and a low level voltage of the scanning pulse generated by the gate driver 130, respectively.
The timing controller 190 supplies a digital video data RGB from a digital video card (not shown) to the data driver 120 while generating a data driving control signal DCC, a gate shift clock GSC and a gate driving control signal GDC using horizontal/vertical synchronizing signals H and V in response to a clock signal CLK. The data driving control signal DCC is supplied to the data driver 120. The data driving control signal DDC includes a source shift clock SSC, a source start pulse SSP, a polarity control signal POL and a source output enable signal SOE. The gate shift clock GSC and the gate driving control signal GDC are supplied to the gate driver 130. The gate driving control signal GDC includes a gate start pulse GSP and a gate output enable signal GOE.
FIG. 3 shows a configuration of a light emitting diode string included in the backlight assembly of the related art liquid crystal display device. As shown in FIG. 3, a light emitting diode string 150 of the related art backlight assembly consists of a plurality of light emitting diodes LED1-LEDn serially connected to each other. Since the plurality of light emitting diodes LED1-LEDn are connected in series with each other, when any one of the plurality of light emitting diodes LED1-LEDn fails as an open circuit, the string of light emitting diodes is turned off. For example, if a second light emitting diode LED2 of the plurality of light emitting diodes LED1-LEDn fails as an open circuit, then the light emitting diodes LED3-LEDn will be turned off.